BIOL 2005 Lecture Notes - Yolk Sac, Ductus Arteriosus, Umbilical Vein
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Published on 30 Jan 2013
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Outline of Lecture 06
Heart Development
Heart has a “nervous system”, the conduction system, in addition to spontaneous
contractility
I. Early heart development
- At days 19-21, cardiogenic cords of the splanchnic mesoderm give rise to two
endocardial tubes, embryonic folding allows apposition and fusion to form heart
tube
- Heart tube is surrounded by ventrally located pericardial sac
- The cardiac mesentery is the dorsal mesocardium; it disintegrates, leaving heart
tube suspended and forming transverse pericardial sinus
- Heart tube consists of endothelium, cardiac jelly, myocardium, epicardium
(inner to outer)
- In week 3, the heart tube loops and fetal blood circulation begins
II. Development of the heart
- 4 divisions of the heart tube: bulbus cordis, primitive ventricle, primitive atrium,
sinus venosus
- Right atrium
- Primitive atrium pectinate muscle in right auricle
- Sinus venosus sinus venarum
- Left atrium
- Primitive atrium left atrium
- Pulmonary veins sprout, branch, and head toward lungs
- Interatrial septum
- Moon-shaped septum primum separates atria; right-left shunt first provided by
foramen primum, then by foramen secundum
- Septum secundum forms with foramen ovale shunt (later becomes fossa
ovalis)
- Together foramen secundum and foramen ovale provide atrial shunt, after birth
fusion of septa closes shunt
- Left and right ventricles
- Primitive ventricle left ventricle
- Bulbus cordis most of right ventricle, conus arteriosus, truncus
arteriosus
- Interventricular septum
- Initially, muscular interventricular septum grows to just below AV canal,
leaving interventricular foramen
- Spiral-shaped conotruncal septa form, dividing outflow tract into aorta and
pulmonary trunk; fuses with membranous interventricular septum
III. Fetal circulation (see table p. 10 for embryonic/adult relationships)
A. Three paired veins
- Vitelline veins: drain yolk sac, related to liver/portal system